Extenders produce a telephoto effect by effectively multiplying the focal length of the lens. They mount between the camera and the other lens. A 1.4x extender multiplies the focal length by a factor of 1.4, which would make a 200mm lens behave like a 280mm lens. The aperture is also affected. The effective aperture is increased by 1 stop, which means that an aperture of 2.8 would become an aperture of 4.0. A 2x extender multiplies the focal length by 2 and adds 2 stops to the aperture. They are designed to mount on prime lenses of 100mm or longer, and all the 70-200mm lenses. They will not mount on wide-angle prime or zoom lenses. Rent a macro camera lens with your next order to add some reach to your photo shoot.